吉林九台营城组孢粉组合及古植被、古气候探讨

PALYNOMORPH ASSEMBLAGES FROM THE YINGCHENG FORMATION, JIUTAI, JILIN

营城组为一套火山岩、火山碎屑岩夹含煤地层,其时代一直存有争议。本文研究了吉林省九台羊草沟煤田4个钻孔中营城组上、下段的孢粉化石,经鉴定计有60属103种,现描述16属22种,包括1个新种。根据孢粉组合的分析,认为营城组下段时代为早白垩世Berriasian期,上段为Valanginian—Hauterivian期。早白垩世该区发育以松科、罗汉松科为主,兼有麻黄科、掌鳞杉科及海金砂科、桫椤科、卷柏科、蚌壳蕨科、莎草蕨料、水龙骨科等多种蕨类植物繁茂的植物群,气候属温暖湿润的亚热带型。

The present paper reports for the first time the sporo-pollen assemblages from the Yingcheng Formation, Jiutai, Jilin, one of the main Mesozoic volcano-sedimentary formations in the Songliao Basin. Abundant pollen grains and spores together with some acritarchs occur in 11 samples of 4 bore holes; those pollen grains and spores together with some acritarchs occur in 11 samples of 4 bore holes; these fossils may be assigned to 60 genera and 103 species. Here described are 16 genera and 22 species, including 1 new species, Lavisporites jiutaiensis.In the palynomorph assemblage from the Lower Member of the Yingcheng Formation, pollen grains of Gymnospermae are dominant, amounting to 66.70％ of the total number of the assemblage, while Pteridophyta spores are 31.92％, but acritarchs are rare (1.38％). Among the gymnosperms, the disaccate pollen grains of Coniferales are most abundant(37.47％); the next ones are those of Cycadopites(11.99％), Ephedripites (6.62％) and Classopollis (3.42％). Among the fern spores, the genera Cyathidites and Leiotriletes amount to 15.24％, while the Lygodiaceae are 2.66％, including the genera Cicatricicosisporites, Klukisporites and Pilosisporites. In this assemblage there are important elements such as Cicatricosisporites Phymatochilus, C. tersus, Pilsisporites verus, Contignisporites mitriforminus, Polycingulatisporites irregularis, Triporoletes reticulatus, Cooksonites erenensis and Jiaohepllis verus. Most of these species have only been reported from the Lower Cretaceous, especially in Northeast China, Europe and North Asia. It is noteworthy that many species occurring in this assemblage have a wider stratigraphic range from Jurassic to Cretaceous, such as Lycopodiumsporites austroclavadites, Foveosporites canalis, Klukisporites pseudoreticulatus, Leptolepidites verrucatus, Uvaesporites Callialasporites dampieri and Eucommiikites troedsonii. As a whole, the Lower Member of the Yingcheng Formation may be assigned to Early Cretaceous, and most probably to Berriasian in age.The assemblage from the Upper Member of the Yingcheng Formation is still richer in sporo-pollen components, with the pollen grains of Gymnospermae amounting to 55.58％and the fern spores to 44.11％, but with only two specimens of angiospermous pollen grains found. Among the gymnosperms, although the disaccate pollen grains of Coniferales are rather diminutive, they still occupy 21.92％, together with the pollen grains of Cycadopites(4.47％), Classopollis (5.08％)and Ephedripites(1.93％). Among the fern spores,Cyathidites and Leiotriletes amount to 13.71％;the Lygodiaceae spores are much more abundant than in the Lower Member of this formation, amounting to 13.71％, including 4 genera and 7 species. In this assemblage, stratigraphically significant species are Appendicisporites tricornitatus,Cicatricosisporites augustus,C. amalostriatus,C.australiensis,Klukisporites pseudoreticulatus, Lygodiumsporites torisimilis, Polycingulatisporites irregularis, p. reduncus, Schizaeoisporites,certus Jiaohepollis verus, etc. , mostly representing typical Early Cretaceous. Therefore, the Upper Member of the Yingcheng Formation is assigned to Early Cretaceous,probably of the Valanginian—Hauterivian age.Based on the composition of the sporo-pollen assemblages from the Yingcheng Formation,it may be inferred that during the Berriasian—Hauterivian epoch,the vegetation in this area was rich, including Lycopodiaceae, Selaginellaceae, Osmundaceae, Lygodiaceae, Schizaeaceae, Dicksoniaceae, Matoniaceae ( or Dipteridaceae ), Polypodiaceae, Podocar-paceae, Pinaceae, Taxodiaceae, Cheirolepidiaceae, Chiamydospermatopsida and Ephedraceae, and occasionally including Angiospermae. At that time, the climate was rather warm and wet ,probably of the subtropical type.